Synthesis of locked nucleic acid derivatives

Abstract

The invention relates to a novel strategy for the synthesis of Locked Nucleic Acid derivatives, such as α- L -oxy-LNA, amino-LNA, α- L -amino-LNA, thio-LNA, α- L -thio-LNA, seleno-LNA and methylene LNA, which provides scalable high yielding reactions utilizing intermediates that also can produce other LNA analogues such as oxy-LNA. Also, the compounds of the formula X are important intermediates that may be reacted with varieties of nucleophiles leading to a wide variety of LNA analogues.

1. A method for the synthesis of a compound of formula IV 
       
         
           
           
               
               
           
         
       
       wherein
 X is O; 
 Z is S; 
 B is a nucleobase; 
 R 3  is selected from —R H , —N 3 , —NR H R H* , —NR H C(O)R H* , —C(O)NR H R H* , —OR H , —OC(O)R H , —C(O)OR H , —SR H , —SC(O)R H , and tri(C 1-6 -alkyl/aryl)silyloxy; 
 each R H  and R H*  independently being selected from hydrogen, optionally substituted C 1-6 -alkyl, optionally substituted aryl, and optionally substituted aryl-C 1-6 -alkyl; 
 A 4  and A 5  independently are selected from C 1-6 -alkylene; and 
 R 5  is selected from iodo, bromo, chloro, C 1-6 -alkylsulfonyloxy, cyclohexanesulfonyloxy and cyclopentanesulfonyloxy, each optionally substituted with one or more halogen, and arylsulfonyloxy optionally substituted with one or more substituents selected from nitro, halogen, C 1-6 -alkyl, and C 1-6 -alkyl substituted with one or more halogen; 
 
       said method comprising the following steps:
 treating an intermediate of the formula I: 
 
       
         
           
           
               
               
           
         
       
       wherein
 X, B, R 3 , A 4 , and A 5  are as defined above; 
 R 2  is selected from iodo, C 1-6 -alkylsulfonyloxy optionally substituted with one or more halogen and arylsulfonyloxy optionally substituted with one or more substituents selected from nitro, halogen, C 1-6 -alkyl, and C 1-6 -alkyl substituted with one or more halogen; R 3  and R 2  may together form an epoxide and R 4  and R 5  independently are as defined for R 5  above, or R 4  and R 5  together constitutes a tetra(C 1-6 -alkyl)disiloxanylidene group; 
 with a nucleophile selected from Na 2 S and potassium thioacetate, so as to substitute R 2 , and 
 effecting ring-closure between the C2′ and C4′ positions under the influence of lithium hydroxide in a polar aprotic solvent so as to yield the compound formula IV. 
 
     
     
       2. The method according to  claim 1 , wherein
 R 2  is selected from C 1-6 -alkylsulfonyloxy optionally substituted with one or more halogen and arylsulfonyloxy optionally substituted with one or more substituents selected from nitro, halogen, C 1-6 -alkyl, and C 1-6 -alkyl substituted with one or more halogen; 
 R 3  is optionally substituted aryl(C 1-6 -alkyl)oxy; and 
 R 4  and R 5  are independently selected from C 1-6 -alkylsulfonyloxy optionally substituted with one or more halogen an arylsulfonyloxy optionally substituted with one or more substituents selected from nitro, halogen, C 1-6 -alkyl, and C 1-6 -alkyl substituted with one or more halogen. 
 
     
     
       3. The method according to  claim 1 , wherein A 4  and A 5  are methylene. 
     
     
       4. The method according to  claim 1 , wherein R 4  and R 5  are identical. 
     
     
       5. The method according to  claim 1 , wherein B is selected from adenine, guanine, 2,6-diaminopurine, thymine, 2-thiothymine, cytosine, methyl cytosine, uracil, 5-fluorocytosine, xanthine, 6-aminopurine, 2-aminopurine, 6-chloro-2-amino-purine, and 6-chloropurine, R 2  is selected from C 1-6 -alkylsulfonyloxy substituted with one or more halogen, R 3  is benzyl, and R 4  and R 5  are independently selected from C 1-6 -alkylsulfonyloxy optionally substituted with one or more substituents selected from halogen and C 1-6 -alkyl substituted with one or more halogen. 
     
     
       6. The method according to  claim 1 , wherein R 4  and R 5  are independently selected from methanesulfonyloxy, trifluoromethanesulfonyloxy, ethanesulfonyloxy, 2,2,2-trifluoroethanesulfonyloxy, propanesulfonyloxy, iso-propanesulfonyloxy, butanesulfonyloxy, nonafluorobutanesulfonyloxy, pentanesulfonyloxy, cyclopentanesulfonyloxy, hexanesulfonyloxy, cyclohexanesulfonyloxy, 2-chloro-α-toluenesulfonyloxy, ortho-toluenesulfonyloxy, meta-toluenesulfonyloxy, para-toluenesulfonyloxy, benzenesulfonyloxy, ortho-bromobenzenesulfonyloxy, meta-bromobenzenesulfonyloxy, para-bromobenzenesulfonyloxy, ortho-nitrobenzenesulfonyloxy, meta-nitrobenzenesulfonyloxy, and para-nitro-benzenesulfonyloxy. 
     
     
       7. The method according to  claim 1 , wherein the intermediate has the formula III 
       
         
           
           
               
               
           
         
       
       wherein B, R 4  and R 5  are as defined in  claim 1 , and wherein R 3  is —OR H  or —OC(O)R H , where R H  is as defined in  claim 1 . 
     
     
       8. The method according to  claim 1 , wherein B is selected from adenine, guanine, 2,6-diaminopurine, thymine, 2-thiothymine, cytosine, methyl cytosine, uracil, 5-fluorocytosine, xanthine, 6-aminopurine, 2-aminopurine, 6-chloro-2-amino-purine, and 6-chloropurine,R 3  is benzyl, and R 4  and R 5  are both methylsulfonyloxy.